Pen cap



FIG. 1 is a lower front left perspective view of a pen cap showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a left side elevation view thereof, with the right side elevation view being a mirror image of the left side elevation view;

FIG. 4 is a rear elevation view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken lines shown in FIG. 6 illustrate environmental subject matter and form no part of the claimed design. 

CLAIM The ornamental design for a pen cap, as shown and described. 